


Caging the Bird

by snasational



Series: Raffle Prizes [2]
Category: Undertale (Video Game)
Genre: Alternate Universe - Angels & Demons, Angel Blue, Demon King Nightmare, Dreamtale Nightmare Sans - Freeform, Graphic Rape/Non-Con, M/M, Underswap Sans (Undertale)
Language: English
Status: Completed
Published: 2021-01-01
Updated: 2021-01-01
Packaged: 2021-03-11 02:34:05
Rating: Explicit
Warnings: Rape/Non-Con
Chapters: 1
Words: 2,540
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28477728
Author URL: https://archiveofourown.org/users/snasational/pseuds/snasational
Summary: The Demon King Nightmare has become smitten with Blue, an angel from another universe. His response?To cage the bird, of course.
Relationships: Sans/Sans (Undertale)
Series: Raffle Prizes [2]
Series URL: https://archiveofourown.org/series/2081718
Comments: 1
Kudos: 59





	Caging the Bird

**Author's Note:**

  * For [SorrowfulRoses](https://archiveofourown.org/users/SorrowfulRoses/gifts).



> I had fun with this raffle! It was a pretty neat AU to write for~ 
> 
> PLEASE read the tags!!!!!!!!
> 
> Not proofread or betad

Blue stumbles as he turns a corridor. His soul beats fast, fear coursing through him as he walks briskly through the castle. His legs ache from running so much, and the fear makes his breathing pick up at an erratic pace. Being brought here against his will was one thing, being chased down in a castle full of murderers was another. 

After a while, he collapses. His body can’t handle running anymore. The exhaustion paired with the wounds he got in the battle before he was captured have taken its toll on him. Blue’s ribcage heaves with breaths he doesn’t technically need, but it helps cool his overheated bones off. The skeleton’s face is pressed against the hard stone and he tenses so hard that his wings begin to ache from where they’re folded against his back. 

One beat, two beats, silence. No footsteps approach him, and Blue can’t feel any of the telltale signs of distorted magic that signifty a shortcut. It seems that he truly is alone. 

Blue lets out a relieved breath. Nobody has followed him. After a few moments of simply laying there, he pushes himself up on shaky legs. The terror of being caught still lingers, but now that he knows he’s relatively safe, curiosity takes ahold of him. 

The castle, once you get over who owns it, is kind of cool. Blue has always loved medieval looking stuff. One of the many reasons why he adored visiting the Angel Queen, back in his timeline. He simply could not get enough of the pretty architecture. The Demon King’s lair seems to faintly resemble that of the Dreemurr castle.

He hesitantly wonders from room to room, taking in the covered furniture and beautiful stonework. It’s gorgeous, everything holds a rustic charm that makes him want to take pictures. Sadly, his phone was left in his world before he was snagged by the King and his demonic minions.

For what reasons, he has no idea. All Blue knows is that he has to get the fuck out of here as soon as he possibly can. Lingering does not seem like a good idea. But...well, he can’t help it! He’ll look at a few more rooms before finding an exit. He hasn’t been found yet, and by this point he doesn’t think he will be. 

He figures that the king wouldn’t let a prisoner roam freely in his castle, so he must be actively looking for him. It would be cruel to watch as Blue wonders around, thinking that he’s safe. From what Blue knows about the guy, he doesn’t really believe that it’s his style. Although...he doesn’t really know him at all.

Blue sighs softly, and then winces as the action reminds him of the bruises blossoming on his ribcage. The adrenaline had nearly made him forget about them. Stars, the lot of them were unnecessarily brutish in their kidnapping. At the memory of the nasty injuries he left on the Sans with the leaky eyes, he grins. 

Just because he’s small and helpless looking doesn’t mean he actually is. Alphys has always praised him for his strength and speed, both on the ground and in the air. It truly goes to show when he actually fights with all he’s got. Nightmare and his minions had an unfair advantage, though. There’s no way Blue could win a fight against four other versions of himself. 

He opens another door and tiptoes inside. This time it’s a bedroom. A really big one, at that. Pressed against the wall in front of him is a four poster bed. The light that filters in from the opened door reveals green curtains tied to the columns of the bed. Personally, Blue thinks his rocket ship bed looks cozier. 

He shuffles even further into the room. Even in the poor lighting, he can make out a tea table in the corner and a gigantic wardrobe next to it. It reminds him vaguely of a Disney movie he managed to get his hands on for Papy when he was younger. Beauty and the Beast, the skeleton remembers. Blue tries to imagine all of this elegant furniture coming to life and giggles lightly at himself. What a silly thought to have!

“You make such pretty noises, little birdy.” 

Blue freezes. 

A voice much deeper than his own chuckles. “Aw, are you shy? Don’t be.” The words are spoken right next to his ear-canal. Blue flinches violently, horror gripping his soul as he spins around to face that voice.  _ Nightmare,  _ his head supplies for him. The very king he’d been running from in the first place. 

Blue readies himself to attack once again despite having a depleted magic pool. However, before he can do anything, tentacles wrap around both of his humeruses.They’re slimy, and gross, and  _ cold.  _ But worst of all, the wretched things cut off his flow of magic. 

Blue cries out, panicked. His wings flap about violently. “Let me go!” He yells. 

Nightmare clicks his tongue, displeased with the struggling. “Would you kindly relax? I am not going to harm you.”

“I don’t believe you!” He’d be a fool if he did. “If you didn’t want to hurt me, you wouldn’t have dragged me here in the first place.” 

He smirks and tilts his head, clearly amused. “Aren’t you so smart?” He praises condescendingly. “But i’m afraid you’re incorrect, I truly have no plans to bring you pain.”

“Liar.” Blue hisses. He jerks his arms, but the tentacle’s hold remains strong. “You will not deceive the Magnificent Sans with your honeyed words. You and your subjects are nothing but bad news.” 

Nightmare narrows his eyes but that awful smile never leaves his face. It sends shivers up his spine. “How hurtful.” He cooes. “You’re certainly not one to be fooled easily. My plans for you aren’t to inflict any physical harm.” 

Blue scoffs. His scarf and cape were torn off of him in the fight, and his shirt is ripped from being grabbed at. Every bit of bone visible to the eye is covered in some sort of wounds. From his neck to what is visible of his ribs. And his poor wings...after the initial flail, they had gone limp at his back. “What a fantastic job you’ve done so far, then!”

“You act as if those were my doing.”

Blue pauses. He’s got a point, all Nightmare did was create the portal that brought them here. His subjects were the ones that had to fight Blue into submission. And even then, it was less giving up and more being ganged up on and shoved into the portal. Did they actually believe he’d go with them and not fight tooth and nail? What did these guys take Blue for, an idiot?

“They were under your command, though.” Blue points out. 

Nightmare rolls his eye. “If you had come with us willingly then they wouldn’t have had to hurt you.”

“You attacked my  _ brother!”  _ He balks. “Are you insane? Why would I have gone with you after you did that!” 

The other skeleton sneers at the mention of Papy. “He was in the way. Regardless, if that superficial damage is truly an issue, I will heal you.”

Superficial? Blue can’t breath without his bones aching! “Don’t touch me! I’ll do it myself, release me.” 

But Nightmare has already begun channeling healing magic through his tentacles. It makes the appendage glow a sickly green, and the magic entering his body is unusual. It’s not comforting or calming like healing magic should be, but nonetheless it gets the job done. Begrudgingly, Blue is thankful that his injuries have been healed. Even if, for some unimaginable reason, he had left his wings damaged. 

“I...Thank you for healing me, but you must let me go. If you don’t wish to harm me then there’s no reason for you to have even captured me in the first place.” Nightmare doesn’t let go. In fact, those tentacles squeeze even harder. The black ooze that coats his corrupted body slides down his arms and Blue cringes. 

“Wrong, once again. But, you have a fantastic intuition. After all, why would you have stepped into this bedroom if you didn’t know my intentions?” 

Blue’s face twists in confusion. “What?”

“Don’t play coy, birdy.” Nightmare pulls him closer until Blue can feel his breath. Up close, Blue can get a glimpse of stained gold that must make up his crown. That cyan eyelight studies him, and Blue finally understands what felt so off about their interaction. 

It’s as if that eyelight is undressing him. 

Fear hits him harder than before. “No! No, you’re the one that’s wrong!”

But Nightmare isn’t listening to him. He leans in and plants his teeth against Blue’s. The angel jerks, but the tentacles don’t allow him to move. Unwanted magic buzzes at the contact. Blue closes his eyes tightly, unwilling to watch this playout. 

“So cute.” The king murmurs. He leans away from the forced kiss and strokes Blue’s face. It smears oil everywhere. “So precious. You’re going to make me the perfect heir.”’

Blue tries not to cry. He really does, but despite his best efforts liquid magic builds up at the corner of his eye sockets. “No. I don’t want that. I don’t want you to touch me. Let me go, please.  _ Please.”  _

“Shh, birdy. I’m going to take such good care of you.” Those tentacles lift him up and Nightmare guides him to the bed. His eyes snap open at this, and he watches with wide eyelights as they approach it. The piece of furniture had once looked neat, but now the sight of it fills Blue with intense dread. Deceptively gentle, the tentacles lower him onto the silk covers. They’re the same color as the curtains, Blue notes in his panic. His wings are sprawled out beneath him and now he’s completely vulnerable to this monster’s whims. 

“You don’t have to do this.” Blue practically sobs. A tentacle comes close to him and wipes his tears away. 

“Don’t be scared. I’ll be gentle.” 

Blue’s still a virgin. Perhaps a bit naively, he was waiting for someone special to take it. Blue is highly educated on the topic of sex, having studied it for when that person came into his life. He wanted the moment to be just as perfect for them as it would be for him, after all. 

Monsters that love each other have sex. What’s about to happen...it’s not love. No, it’s something brought on by this freak’s sick fascination with him. The reality that his first time is going to be brought on by rape causes him the begin thrashing wildly. He kicks his feet at Nightmare.

“Will you cut that out?” He hisses. “You should be honored that I have chosen you. Show a little appreciation for your king.” 

More tentacles wrap around his femurs, holding him still. Nightmare has to bend his spine to accomplish this, and now he hovers over Blue menacingly. Blue trembles at this new development. 

“No!” He wails. “I didn’t agree to this!”

The demon chuckles darkly. “That hardly matters.” 

Hands grips at his pants and pulls. Thanks to Nightmare’s unnatural strength, the thread tears easily and reveals to him Blue’s pelvis. He shrinks under the weight of that gaze. “Relax and enjoy this, birdy.” He purrs. 

Oily phalanges play with the bone, tracing the curves and caressing the dips. 

The fight leaves the angel all at once and he goes limp on the sheets. This is going to happen no matter what he does. The king has so many advantages against him. Nobody is going to save Blue. 

“There we go. Such a good birdy.”

Magic reacts to Nightmare’s touch. Blue stares up at the ceiling of the four poster bed and starts trailing the lines of wood. He wonders if the bed is made of authentic wood like his rocket ship one is. Papy hand made it. His brother is super talented, even if he’s lazy. A finger dips into his entrance and Blue feels like throwing up. 

He should make Papy a race car bed. Those are super cool. And then they can both have themed beds. Matching is always fun. 

Another finger. They pump in and out. 

Papy goes along with anything. If Blue said he wanted to match then he’d definitely agree. Blue starts budgeting materials in his head. Wood and paint doesn’t come cheap. And he’d probably need to find blueprints, somewhere. Or he could use his imagination. Yeah, that sounds like fun. 

They pull out. Blue tenses. 

Where was he? Right, the materials. He wonders which type of wood runs the cheapest. He’s definitely going to have to-

His eyes snap open and he screams at the sensation of being filled. Something inside his forcibly summoned pussy tears and it sends pangs of pain throughout his entire lower body. His eyelights quickly trail down.

Holy shit. 

Through the thin layer of light blue magic, he can make out the enormous shape of Nightmare’s monstrous cock. It takes the form of another tentacle, and he can both feel and see the way it squirms. When he pulls out to thrust back in, Blue can see his blood coating the dick.

It is the most agonizing thing he’s ever experienced before in his life. Blue throws his head back and screams. The tears have made their appearance again. It makes a mess out of his face.

Nightmare groans. “You feel divine, my little angel.” 

Blue’s breathing comes out as hiccups. “Please, please! Out, pull it out! Get it out of me, it hurts so much!” 

“Shh,” He shushes. That hand comes to rest on his face again. Slick and disgusting like the rest of him. “First times are always the worst. It will get better, I promise.”

At the implication of there being more times, his soul constricts. Is he ever going to get to see his brother again? His home? Will he ever fly in the sky with Alphys, will he ever get to sit with the Angel Queen as she waters her buttercups? 

A small crack forms in his soul, devastation seeping into his very being. 

But Nightmare does not notice, nor does he care. He thrusts inside Blue’s abused cunt with abandon. The tentacles pull him into every thrust and the slap of magic hitting magic fills the room along with the cries of Blue. 

Suddenly, he tenses and trembles. The demon’s cock gives a violent twitch, cum spurting out and coating Blue’s magic in its essence. The feeling of it disgusts Blue. It’s unnatural. None of this is supposed to happen. He begs his magic not to take to the seed. In the aftermath of an angel and a demon breeding, there would be the creation of a Nephalem. Horrid creatures. Blue wants no part in it. 

Nightmare stays inside him as he drapes himself over Blue’s quivering form. “You were so lovely, my little birdy.” He whispers. A tongue slivers out of his jaw, long and purple and nasty. It licks away Blue’s tears.

“Why me?” Blue asks hoarsely. “Why did you do this to  _ me?”  _

Nightmare only grins in response. 

**Author's Note:**

> Follow me on twitter @ snasational 
> 
> Comments & Kudos are always appreciated!


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